This invention relates to compositions and methods for inhibiting the actions of non-coding RNAs such as miRNAs and piRNAs.
RNA interference (“RNAi”) is a near-ubiquitous pathway involved in post-transcriptional gene modulation. The key effector molecule of RNAi is the microRNA (“miRNA” or “miR”). These small, non-coding RNAs are transcribed as primary miRNAs (“pri-miRNA,”), shown in FIG. 1, and processed in the nucleus by Drosha (a Type III ribonuclease) to generate short hairpin structures called pre-miRNAs. These molecules are then transported to the cytoplasm and processed by a second nuclease (Dicer) to generate the mature, duplex form of the miRNA which is then capable of being incorporated in the RNA Induced Silencing Complex (“RISC”). Interactions between the mature miRNA-RISC complex and target messenger RNA (“mRNA”) are (in part) mediated by the seed region of the miRNA guide strand (nucleotides 2-7) and lead to gene knockdown by transcript cleavage and/or translation attenuation.
Tools that enable researchers to understand the roles that miRNAs and miRNA targets play in disease, cellular differentiation, and homeostasis are invaluable. Such tools include but are not limited to miRNA inhibitors. Classes of miRNA inhibitors have been previously described (see Meister 2004 and Hutvagner 2004). These molecules are single stranded, range in size from 21-31 nucleotides (“nts”) in length, and contain O-methyl substitutions at the 2′ position of the ribose ring. Since the original discovery of miRNA inhibitors, multiple design elements have been identified and incorporated to enhance the efficacy of these molecules in a biological setting. For example, it has been demonstrated that inhibitors that have longer lengths or incorporate secondary structures (e.g. double stranded inhibitors) exhibit superior performance over the shorter 21-31 single stranded nucleotide design (Vermeulen et al. 2007). Other designs include the incorporation of locked nucleic acids (“LNAs”) (Orom et al. 2006).